Rotating beam missile guidance system



March 17, 1970 G. J. R. MACLUSKY 3,501,113

ROTATING BEAM MISSILE GUIDANCE SYSTEM Filed Jan. 2, 1968 2 Sheets-Sheet 1 lnvenlor mww J EPH M M L,

March 17, 1970 G. J. R. MACLUSKY 3,501,113

ROTATING BEAM MISSILE GUIDANCE SYSTEM 2 Sheets-Sheet 2 Filed Jan. 2, 1968 u 2Q Quid? R m 1 H Q. 211 Q 5% $6M 1111 r.

GORPGN (TOSEPH REDMR/V MAQ Y US. Cl. 2443.13 2 Claims ABSTRACT OF THE DISCLOSURE A missile is guided by a beam radiated in the required direction of flight. The beam comprises a rotating pattern of radiation. The missile is rotated about its axis during flight and a radiation detector is mounted on the missile oflset with respect to its axis of rotation. When the missile flight path is offset with respect to the axis of rotation of the pattern of radiation, the detector output includes a frequency modulated component which is used to guide the missile back towards the beam pattern axis.

This application is a continuation-in-part of application Ser. No. 417,244, filed Dec. 9, 1964, and now abandoned.

It has previously been proposed to guide a short-range missile along a beam of light or microwave energy which is aimed at a target. In one prior proposal, departure of the missile from the required direction was detected by the fluctuations of signal amplitude at two antennas on the missile caused by sweeping the beam of electromagnetic energy to form a cone having the said direction as its axis. The required direction of corrective movement was ascertained from the phase difference between the signals at the two antennas.

The object of the present invention is to provide a beam-riding system which is relatively simple and is insensitive to all effects producing only amplitude modulation of the beam.

According to the present invention this is achieved by guiding the missile in a pattern of infra-red, visible or ultra-violet radiation which is rotating about an axis leading to the target and by providing in the missile means for rotating the missile about its axis during flight, a detector, responsive to the radiation, which is mounted on the missile offset with respect to the missile axis, and means receiving the detector output and responsive to the frequency modulation of the latter resulting from the rotation of the radiation pattern and the rotation of the offset detector to adjust flight path controls and hereby to steer the missile towards the pattern axis. The rotating radiation pattern may be provided by means of a projector, external to the missile, for aiming a beam of infra-red, visible or ultra-violet radiation at the target and a rotary pattern device for splitting the beam crosssection into sectors and for rotating the sector pattern. The frequency modulation occurs when the missile is offset with respect to the beam axis because the circular movement of translation of the detector is in the same direction as that of the sector pattern for one-half of the missiles rotary movement and is opposite to the motion of the sector pattern for the other half of its rotary movement. It will be understood that the expression sector pattern is not intended to restrict the pattern to sectors defined by the radii of a circle and that it will include, for example, the case in which the patterning device includes a number of curved sections extending from its centre to its periphery.

The invention thus provides a simple means of guiding a missile along the beam. It is not necessary to use a roll reference gyroscope in the missile and this allows a veiy high launch acceleration to be used without danger of damage to the gyro or of causing it to develop excessive drift. In addition, as the modulation of the detected signal is frequency or phase modulation, the system is insensitive to all effects producing only amplitude modulation of the radiation, such as atmospheric and smoke attenuation and variation of distance between the missile and the beam projector.

In order that the invention may be better understood one example will be described with reference to the accompanying drawings, in which:

FIGURE 1 illustrates the missile in the radiation pattern;

FIGURE 2 projector;

FIGURE 3 is a block diagram of the missile flight control system, and

FIGURE 4 shows a simple form of actuator for the missile elevators.

In FIGURE 1 there is shown a missile 1 travelling into the plane of the paper and a beam axis 2 towards which the missile is to be deflected. The beam of flight along which the missile is to be steered towards the target is assumed to have its axis perpendicular to the plane of the paper. This beam is split by a rotating pattern device into a large number of sectors, of which only about one half are shown in the drawing, which rotate about the beam axis at a constant frequency. It will be seen that the missile is offset with res ect to the beam axis in this example on the side on which the sectors have been shown.

The missile carries two arms 5a and 5b which have at their ends a light-sensitive detector 3 and a balance weight 4 respectively. It is also provided with fins 6 and 7 which turn about an axis transverse to the longitudinal axis of the missile and thereby control the flight path of the missile. The movements of the fins to control the deflection of the missile towards the beam axis are superimposed on equal and opposite standing fin angles which produce a rotation of the missile about its axis. In the example shown in FIGURE 1 the rotations of the sector pattern and the missile are both clockwise. Since the missile is offset with respect to the beam axis, the detector will find itself moving in the same direction as the portion of the sector pattern in which it is located as it traverses the outer portion of the pattern and in the opposite direction as it traverses the portion of the pattern which is nearer to the beam axis. Consequently, the number of sectors of light through which the detector 3 passes in a given period is less while the detector is traversing the outer side of the beam than when moving through the portion of the beam which is nearer to the beam axis. As a result, the output of the detector 3 is modulated in frequency and phase.

The missile includes a control unit containing circuits which convert the modulated signal from the detector into a waveform which, after amplification, controls the movement of the fins 6 and 7. As the missile is spinning about its own axis these fins must be given an oscillatory movement at the frequency of rotation of the missile in order to steer the missile towards the beam axis and this frequency is also the frequency at which the output of the detector 3 is frequency modulated.

When the missile axis coincludes with the beam axis the missile and sector pattern are rotating in the same angular direction, as far as the detector 3 is concerned,

shows diagrammatically the pattern 3 for the whole of its rotation and consequently there is no frequency variation in the modulation of the light signals.

The sector projector is shown diagrammatically in FIGURE 2, in which radiation from a source contained in a projector casing 11 passes through a sector mask 12 driven by a motor 13 and falls on a lens 14. The rotating sector mask acts to divide the light into sectors which rotate about the axis of the beam.

In the missile, the signal from the radiation detector 3 (FIGURE 3) passes through an amplifier 15 to a limiter and frequency modulation detector circui- 16. If the missile path is not on the axis of the rotating beam, the lightsensitive detector will produce a signal of varying fre quency and the frequency modulation detector 16 will generate a corresponding amplitude-varying signal for the actuation of the fins 6 and 7 to superimpose oscillatory angular movements on to the standing angles of the fins to cause translation of the missile towards the pattern axis. The direction of movement of the missile depends on the phase relationship between the oscillatory angular movements and the rotation of the missile about its own axis and therefore the phase relationship between the signals generated by the light-sensitive detector and the rotation of the missile. The frequency of the out put of the light-sensitive detector 3 will be a maximum as it crosses a line joining the missile axis and the beam axis, between these two axes, and a minimum at a point 180 distant from this; the frequency modulation detector will consequently generate maximum signals of opposite polarities corresponding to the passage of the light-sensitive detector 3 through these two points. To cause the missile to move towards the beam axis, for one half of the cycle of rotation of the missile the standing angle of incidence of fin 6 is increased and that of fin 7 is reduced and for the other half the standing angle of incidence of fin 7 is increased and that of fin 6 is reduced. When the line joining the light-sensitive detector 3 and the counterweight 4 passes through the beam axis. in

the absence of a rotation-producing standing angle of the fins they would both be given a displacement towards the axis to cause the missile to be turned towards the axis. In the presence of the equal and opposite rotationproducing standing angles of the fins, in this position of the missile the incidence of one fin is increased and the opposite incidence of the other is decreased. giving rota tion together with a displacement of the missile towards the beam axis. As the missile rotates, the fins first return to their standing angles and then move in directions opposite to their first directions of movement.

It is an advantage of the arrangement that the signals from the detector are already varying at the required frequency of oscillation of the fins and that once a suitable phase relationship is obtained between the fin oscillatory movement and the waveform of the same frequency at the output of the frequency modulator detector, the phase of the waveform is automatically correct for ensuring that wherever the missile is located in the pattern the corresponding oscillatory movement of the fins will deflect the missile towards the beam axis. The signals from the frequency modulation detector 16 are therefore simply passed through an amplifier 17 to an actuator unit 18 for angularly adjusting the fins.

A simple form of fin actuator is shown in FIGURE 4. The fins 6 and 7 are attached to a crankshaft 21 at standing angles which will provide the required missile rotation. When energised by cylically varying current from the amplifier 17, a solenoid 19 causes an armature 29 to oscillate in a cyclic manner, causing a corresponding turning movement of the crankshaft 21. In turn this causes cyclically varying angular movement of the fins 6 and 7, adding to the standing angle of one and subtracting from that of the other in opposite half-cycles. When the solenoid 19 is de-energised the return spring causes the cranked shaft and the fins to return to their original position which is determined by the stop 22.

Phasing errors resulting from time delays in the control unit or fin actuators can be corrected by rotating the axes of fins 6 and 7 about the missile axis relative to the original position perpendicular to a line joining the lightsensitive detector 3 and the counterweight 4.

The frequency modulation of the guidance signal depends only on the distance of the missile from the guidance axis and is independent of the distance of the missile down the beam from the projector.

The invention can be applied, for example, to a projectile of the bazooka kind. The arms 5a and 5b and the fins 6 and 7 fold away within the body contour for launching but pivot outwards as soon as the projectile has left the launching tube.

In the preferred system the sector pattern rotates with an angular velocity greater than that of the missile. In one example, the sector velocity is 60 revolutions per second and the missile angular velocity 15 revolutions per second. In this example the beam is split into 50 sectors. However, the guidance scheme described above will also operate if the angular velocity of the missile is greater than that of the sector pattern, and/or if the missile rotates in the opposite direction to the sector pattern.

I claim:

1. A short range missile including: flight path controls adjusted to rotate the missile about its axis during flight; a detector which is responsive to infrared, visible or ultraviolet radiation and which is mounted on the missile offset with respect to its axis of rotation so that when the missile is flying in a rotating pattern of radiation and is offset with respect to the axis of rotation of the pattern the detector output will include a frequency modulated component; and means responsive to the frequency modulation of the detector output and arranged to additionally adjust the flight path controls in response to the frequency modulation for steering the missile towards the pattern axis.

2. A missile guidance system for guiding a missile having flight path controls and means for rotating the missile about its axis during flight, the system including: a pro jector external to the missile for aiming a beam of infrared, visible or ultra-violet radiation at the target and a rotary pattern device for splitting the beam cross-section into sectors and for rotating the sector pattern; a detector responsive to the radiation which is mounted on the missile offset with respect to the missile; and means receiving the detector output and responsive to the frequency modulation of the latter resulting from the rotations of the sector pattern and the detector to adjust the flight path controls in response to the frequency modulation and thereby to steer the missile towards the beam axis.

References Cited UNITED STATES PATENTS VERLIN R. PENDEGRASS, Primary Examiner US. Cl. X.R. 2443.l6 

